This installment of CreatureCast is the second of several contributions that were done as final projects by undergraduate students in Casey Dunn’s Invertebrate Zoology class at Brown University. In episode 4, sophomore Noah Rose delves into the bottom half of the circle of life, where dead things decompose and elements that can then be incorporated into other living organisms are liberated. Noah discusses how the many-legged worms we tend to think of as fish bait impact this process.
Bioluminescence can be used for myriad purposes in different species—this recently discovered species of annelid, Swima bombaviridis, probably uses bioluminescence to escape from predators. It was described by Karen Osborn and friends. The worm carries eight fluid-filled packets near its head that it can release at will. When these packets are released, they bioluminesce a bright green for several seconds. Since the worms live in the deep sea, these flashes are a contrast to the dark environment and may distract predators—instead of getting a bite of worm, they are left with nothing. The mechanism for releasing these bioluminescent bombs is unclear—in addition to the lack of light at the depths the worms live at they are without eyes—but the release is probably related to a tactile sensory system, as they release their bioluminescent organs when touched.
Photo by Casey Dunn. The head is to the left, and the green bioluminescent packets can be seen attached to the body just behind it.
Reproduction is a complex business, and often requires that the partners meet. Polychaete worms belonging to Odontosyllis have developed a highly elaborate mating behavior that includes bioluminescent signals. During a recent stopover on the Bermuda islands, on a sailing trip across the Atlantic, I was able to witness the fascinating mating dance of Odontosyllis enopla. The species normally spends its life in shallow water on rocky or sandy bottoms. Once a month, 2-5 days after full moon and around 55 min after the astronomical sunset, the animals start ascending to the sea surface. Here the circling female tries to attract a male by emitting green light and the repeated release of green glowing clouds. The male signals its presence via bioluminescent flashes. In the course of this dance – which may last from 10 to 30 min – the animals spawn and the sea turns black again as they go dark. Remarkably, the worms undergo severe modifications of their body and behavior when switching from the bottom dwelling mode of living to the free floating form. In the case of the males this means, amongst other things, a considerable enlargement of the eyes. After spawning the worms return to the bottom and can potentially swarm again. The photo above, by Greg Rouse, is of the Californian species Odontosyllis phosphorea in its benthic phase. Data from Dimitri Deheyna and Michael Latz suggest the involvement of a photoprotein in the bioluminiscence of this species.
